1. Field of the Invention
This invention relates to packaging machines, and more particularly to such machines as are useful for packaging fluidized dry, divided, solid material into containers such as paper bags, for example.
2. Description of the Prior Art
Constructions of the class described are well known to those skilled in the art, and are exemplified in U.S. Pat. No. 3,261,379 which discloses apparatus including a bin for fluidizing the material to be packaged and a tubular element or conduit for conducting such fluidized material to a filling spout which may constitute the discharge end of the conduit and upon which a bag may be secured to receive a charge of the material. The bag may be weighed and the flow of material cut-off when a predetermined weight is reached, cut-off being effected by pinching a flexible tube forming a portion of the conduit through which the fluidized material moves from the bin to the filling spout.
Attention is also invited to U.S. Pat. Nos. 2,866,484 and 2,955,796 which are concerned with bag filling apparatus and disclose means for effecting a seal between the filling spout and the bag when the spout extends into the valve of a bag thus to minimize the escape of dust from the bag during filling. Such sealing is effected by providing an expansible sleeve around the filling spout, the sleeve being pressurized internally to expand during filling, and relaxed by relieving the pressure upon completion of filling to permit easy removal of the bag.
While the machines and apparatus disclosed in the above mentioned patents have achieved a degree of commercial success, nevertheless, due at least in part to the fact that forces generated by the cut-off device had not been isolated from the weighing section of the device, which section supports the filling spout, it had been impossible to achieve a desired degree of uniformity of weights of filled bags and to checkweigh bags after filling without these external forces influencing the checkweigh readings. To remedy this difficulty, it has been proposed to attempt to isolate the filling spout and weighing mechanism from the rest of the machine by forming part of the flow path between the cut-off mechanism and the filling spout of a length of flexible tubing. This was done simply by clamping one end of a length of rubber tubing to the filling tube and the other end to the adjacent end of the tube or conduit forming the material flow path downstream of the cut-off device. We have found this arrangement to be unsatisfactory because, some unbalanced forces remained adversely to affect the filling and checkweighing results. This unbalance was due to flexure in the cut-off device and in the rubber isolation tube due to pressure variations therein and to mechanically induced flexure in the cut-off device to stop the flow of material to a bag. We also noted that, regardless of how tightly the clamps were set or how large the clamps were, relatively light external forces caused the rubber tubing to shift relative to the conduit thus further aggravating the unbalanced forces acting through the filling spout on the weighing section of the machine and causing non-uniform filled bag weights.
Additionally, when the filling spout and expansible sleeve were inserted into the bag valve and the sleeve inflated to cause it to expand, if the sleeve did not fully enter the valve, as is the case where a pasted valve bag is used, that external portion of the sleeve frequently caused the bag to tear at the valve or caused damage to the sleeve when the sleeve was expanded.